Apparatuses for drying cut wood are divided into two types. One type has a condenser arranged outside the vessel containing the cut wood as shown in DE-PS 309 086. The other type has a condenser disposed inside the vessel containing the cut wood which is to be dried. The separation of the condenser from the vessel containing the cut wood to be dried according to the first type has the advantage that the steam atmosphere in the vessel for drying the cut wood is not cooled by the condenser. However apparatus of the first type has the disadvantages of a substantially higher installation cost and requiring more space for the installation. The combining of the condenser in the vessel according to the second type (DE-PS 35 43 248; DE-OS 37 15 515) requires far less space because the condenser is located in the vessel in a chamber where there is no cut wood. That is because, according to DE-PS 35 43 248 and DE-OS 37 15 515 the condenser is located below the carriage which supports the cut wood to be dried and which runs on rails parallel to the axis of the vessel. With the usual horizontal circulation of the drying medium through the pieces of cut wood stacked one above another, a considerable part of the circulating drying medium moves through the condenser and is cooled to such an extent that a part of its moisture content is deposited on the tubes of the condenser. The drying medium cooled in this manner flows, in its circulation, with the circulating drying medium flowing horizontally through the stack of cut wood and is mixed therewith. Thereby, the continually circulating drying medium is wholly cooled and must be again heated in order to be brought to a favorable temperature for drying. The constant mixing of the drying medium cooled in the condenser with the drying medium flowing through the stack of cut wood results in higher energy consumption by reason of the requirement that the drying medium cooled in the condenser must be again heated. Through U.S. Pat. No. 1,625,548 it is known to use the inner side of the cylindrical vessel wall as a condenser. This vessel wall is cooled by water sprayed on its outer surface while the interior of the vessel is heated by an integrated heat register. The moisture of the steam type drying medium is deposited on the inner side of the vessel wall and runs on the inner side of the vessel wall to the bottom of the vessel and is discharged through a valve controlled tube. So that moisture deposited on upper portions of the vessel wall does not fall on the cut wood that is to be dried, there is arranged over the cut wood a roof which leads the dropping moisture to opposite sides of the vessel. This roof takes room which could serve to hold cut wood. Also there is a disadvantage of a constant mixing of the drying medium deposited on the inner side of the vessel wall with the remaining drying medium so that for the reheating of the cooled drying medium additional heat energy is required.
The drying of cut wood by the known apparatus is relatively expensive because high installation costs must be taken into account and also because of a relatively high cost of the energy requirements.